ADU Rules in Tacoma, Washington

Tacoma is Washington's third-largest city (population ~220,000), the county seat of Pierce County, and an important port city on Commencement Bay and the southern Puget Sound. Tacoma features the Foss Waterway, the Port of Tacoma (one of the busiest on the West Coast), and Point Defiance Park. The city is subject to Washington's major statewide ADU reform, which significantly expands housing options on residential lots.

Washington State ADU Law: HB 1337 (2023)

Washington HB 1337 (2023) is the foundational statewide ADU law that applies to Tacoma. Its core requirements:

• Cities must allow up to 2 ADUs per lot — one attached/internal + one detached — by right on any lot with a single-family home
• No owner-occupancy requirement permitted
• No ADU-specific impact fees allowed
• Cities may not require ADUs to be smaller than 1,000 square feet
• Municipalities face limits on how restrictive their setback, lot coverage, and height standards for ADUs can be

Washington HB 1110 (2023) complements HB 1337 by requiring cities like Tacoma to allow duplexes and other middle housing types in residential zones.

Tacoma is subject to the Washington Growth Management Act (GMA), requiring a comprehensive plan, urban growth area planning, and zoning consistent with growth targets.

Tacoma Local ADU Code

Tacoma's Planning and Development Services administers the local zoning code. Local rules must operate within HB 1337's framework and cannot be more restrictive than state law allows.

Permitted ADU Types

• Detached ADU: A separate structure in the rear or side yard of the lot
• Attached ADU: An addition to the primary home sharing at least one wall
• Internal/Converted ADU: Conversion of basement, garage, or attic space within the existing structure

A lot may have up to 2 ADUs (one attached/internal + one detached) simultaneously.

Size Limits

State law prohibits Tacoma from capping ADUs below 1,000 square feet. Contact Tacoma Planning and Development Services for the current maximum size in your specific zone.

Setbacks

HB 1337 limits Tacoma's ability to impose setbacks that would prevent reasonable ADU construction. Setback requirements vary by zoning district. Verify current standards with Tacoma's Permit Center.

Critical Areas Ordinance (CAO)

Tacoma's CAO protects wetlands, streams, fish and wildlife habitat (including salmon-bearing Puget Sound tributaries), steep slopes, landslide hazard areas, seismically hazardous areas, and frequently flooded areas. Many areas near Commencement Bay and lowland areas carry flood and habitat buffer requirements. Review Tacoma's GIS mapping tools to identify any CAO constraints on your property before designing an ADU.

Mount Rainier Lahar Hazard

Mount Rainier (14,411 feet) is one of the most dangerous volcanoes in North America. In the event of an eruption, volcanic lahars (fast-moving mudflows) could travel rapidly down the Puyallup River valley toward Tacoma and the Port area. Washington DNR publishes lahar inundation maps showing the extent of potential lahar flow paths. Some low-lying areas of Tacoma near the Puyallup River are within mapped lahar hazard zones. While lahar risk does not prohibit development today, it is an important long-term hazard for property owners to understand. Consult DNR's volcano hazard maps at dnr.wa.gov before purchasing property in potentially affected areas.

Seismic Hazard — Cascadia Subduction Zone

Tacoma and the entire Puget Sound region face significant seismic risk from the Cascadia Subduction Zone (CSZ), which could produce a magnitude 9.0+ earthquake. Tacoma has areas with fill soils and soft marine sediments — particularly near the waterfront and Port — that are susceptible to liquefaction during strong shaking. USGS and Washington DNR seismic hazard maps identify liquefaction-prone areas. ADU foundations in these areas require careful geotechnical assessment. All construction must meet Washington State Building Code seismic requirements.

Permit Process

1. Research your property's zoning and CAO constraints via Tacoma's GIS portal
2. Schedule a pre-application conference with Tacoma Planning and Development Services
3. Prepare construction plans meeting Washington State Building Code requirements
4. Submit permit application at tacomapermits.org or in person at 747 Market Street, Suite 345
5. Plan review and permit issuance
6. Construction inspections
7. Final inspection and Certificate of Occupancy

Contact Tacoma Permit Center: (253) 591-5030 | tacomapermits.org

Disclaimer: This guide provides general information based on Washington HB 1337 (2023) and Tacoma's municipal code as of April 2026. Zoning regulations change frequently. Lahar hazard and seismic information is for general awareness only — consult Washington DNR and a geotechnical engineer for site-specific assessments. Always verify current requirements with the City of Tacoma before making development decisions. This is not legal advice.